A screed is a very important work unit of a paving machine, responsible for smoothing and compressing the mixture to eventually form a road surface. In order to conveniently adjust the paving width of the paving machine, some screeds include a telescopic section screed and a main section screed. The telescopic section screed is telescopic in a transversal direction (the horizontal direction substantially perpendicular to the travelling direction of the paving machine, i.e. generally a paving width direction) with respect to the main section screed. The screed comprising a telescopic section screed and a main section screed is called a telescopic screed. Typically, the telescoping direction of the telescopic section screed is the paving width direction. It is also obvious that, for some telescopic section screeds, the telescoping direction and the paving width direction form a slight angle.
Telescopic screeds are usually classified into front telescopic screeds and rear telescopic screeds. The telescopic section screeds of the front and rear telescopic screeds are arranged in the front side and the rear side of the main section screed, respectively, and are telescopic transversely relative to the main section screed.
In addition, in regions such as North America and Australia, cross slopes are usually required on both sides of the road surface (the edges on both sides of the road surface are lower than the middle part of the road surface), so as to facilitate water drainage. FIG. 1 shows a cross-sectional view of such a road surface R, which includes a middle horizontal surface H and the cross slope surfaces S on both sides; the cross slope surface S has a cross slope with respect to the middle horizontal surface H; namely, there is a lateral inclination angle α between the cross slope surface S and the middle horizontal surface H. I represents an intersecting line between the cross slope surface S and the middle horizontal surface H. Therefore, the telescopic screed in these regions typically requires that the telescopic section screed thereof is adjustable in cross slopes relative to the main section screed.
The patent with the publication No. CN100564682C (and the priority No. U.S. 60/452,883) discloses an extension screed (i.e. a telescopic screed), comprising: a main screed (i.e. a main section screed); a base member movably connected with the main screed; a vertical actuator for connecting the main screed and the base member, each enabling the base member to move vertically or to pivot in a vertical plane; an inside framework movably connected with the base member; a first horizontal actuator which enables the inside framework to move horizontally with respect to the base member; an outside framework movably connected with the inside framework; a second horizontal actuator which enables the outside framework to move horizontally with respect to the inside framework; and a telescopic section screed connected with the outside framework. The main drawback of such screed lies in that the vertical actuator is connected in a manner of enabling the base member to move vertically and pivot, so the rigidity between the base member and the main screed becomes very poor, which significantly affects the quality of the paved road surface.
The patent with the application No. CN200910165203 (and the priority No. EP09002132) discloses a paving screed (i.e. a screed), comprising: a base screed (i.e. a main section screed); a base guiding structure pivotally connected to the base screed; a guiding sub-structure being transversely guided in the base guiding structure; a first actuator for enabling the guiding sub-structure to slide by a first stroke with respect to the base guiding structure; an extension guiding structure being transversely guided in the guiding sub-structure; a second actuator for enabling the extension guiding structure to slide by a second stroke with respect to the guiding sub-structure; and a base framework structure connected to the extension guiding structure through the vertical guiding part and the height adjustment assembly. The shortcomings of such screed lie in that there are two sets of guiding structures and two sets of actuators distributed in space, and thus a lot of space is occupied, and the spatial distribution of the two sets of guiding parts weakens the rigidity of the entire telescopic structure, further affecting the paving quality of the road surface.
The patent with the publication No. CN101812823B (the priority No. EP08021844.9) and the patent with the publication No. CN101748680B (the priority No. EP08021843.1) disclose a paving screed (i.e. a screed) and a method for laying a paving mat. The paving screed mainly comprises: a base screed (i.e. a main section screed); a main base plate arranged under the base screed; an extension guiding structure transversely and slidably connected to the base screed through several guiding assemblies; and a framework which is connected to the extension guiding structure through the vertical adjustment assemblies and the driving parts and whose relative height can be adjusted; a telescopic section base plate connected to the framework; a lateral inclination adjustment assembly for adjusting the cross slope of the telescopic section base plate with respect to the main section base plate, arranged between the vertical adjustment assemblies and the framework or between the framework and the telescopic section base plate. Disadvantage of such screed lies in that, when the telescopic section screed telescopes, the lateral positions of the intersecting lines between the cross slope surfaces at both sides and the middle horizontal surface will change, which is not allowed in many paving conditions. Therefore, it is necessary to add a complicated control system for controlling the screed, so as to maintain the lateral positions of the intersecting lines unchanged, which not only substantially increases the cost, but also brings about fault points and unreliability.